'I need PA, natural, best price.' It sounds efficient. But treating PA6 and PA66 as the same material — nylon is nylon — is one of the quieter ways to end up with a part that warps, fails hot, or costs more to fix than the cheaper resin ever saved.
The problem
A buyer looks for 'PA natural' and decides mainly on price, moving between PA6 and PA66 as if they were interchangeable. They share a family, but their behaviour in the part is not the same.
Why it happens
PA6 and PA66 differ in ways that show up exactly where parts are stressed:
- Thermal behaviour — PA66 has a higher melting point and typically better heat resistance; PA6 processes at lower temperatures.
- Moisture uptake & conditioning — both absorb water, but the uptake and the resulting dimensional and mechanical change differ — and affect tolerances.
- Processing window — melt temperatures, crystallisation and shrinkage behaviour are not the same.
- Property profile — stiffness, toughness and surface differ, before you even add glass or additives.
- Viscosity, nucleation, stabilisation, additives — these shift both materials further, so the family name alone says little.
How to choose it properly
Work the application backwards to the material, not the price forward to the part:
- 1Temperature — the service and processing temperatures the part must survive.
- 2Mechanics — the stiffness, toughness and fatigue the part needs.
- 3Geometry — wall thickness, tolerances and how much dimensional change you can accept.
- 4Process — the moulding window you actually run.
- 5Then the material — the PA family, type and additive package that meets all of the above.
Key takeaway
PA6 and PA66 are not interchangeable by name or price. Choose from the part's temperature, mechanics, geometry and process — the cheapest 'PA natural' is only cheap if it makes the part you need.
Buy the material family the application asks for, not the one the label happens to share.
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